1. Field of the Invention
The present invention relates to a resistor for use in an electronic apparatus and a method of making the same.
2. Description of Prior Art
Commonly, electrodes and a resistive body for a square chip resistor are produced in a combination by a thick-layer method including printing and baking steps or vapor deposition and sputtering method. The resistor body is then trimmed by laser to have a desired value of resistance. However, the resistor body when being trimmed by laser may be damaged along the trimmed edge by the heat of laser hence lowering its load or pulse characteristic. For compensation, the resistor body is provided locally with a ladder-like resistance path(s) across which the trimming is made to determine a desired resistance.
The conventional resistor having such ladder-like resistance paths will now be explained.
On example of the conventional ladder-like resistance path equipped resistor is disclosed in Japanese Patent Laid-open Publication No. S60-163402 as shown in a plan view of FIG. 19. As shown, there are provided a substrate 1 made of alumina, electrodes 2 made of nickel-chromium and gold and located on both side ends of the substrate 1 to extend from the upper surface to the lower surface, and resistor bodies 3, 4, and 5 made of a tantalum thin film and located on the upper surface of the substrate 1 between the two electrodes 2. More specifically, denoted by 3 is a main resistance path while 4 and 5 are ladder-like resistance paths arranged in parallel to the main resistance path 3. The ladder-like resistance path 5 is greater in the cross section of the resistive body then the ladder-like resistance path 4. Denoted by 6 are slit grooves made by laser trimming for slitting the ladder-like resistance paths.
A method of making the conventional resistor is explained.
First, layer patterns of tantalum thin-film resistor body and nickel-chromium/gold electrode element are formed on the substrate 1 made mainly of 96% pure alumina with a known magnetron sputtering apparatus.
The resistive body and the electrodes are then shaped by a photo-etching technique and heated at 350.degree. C. for one hour.
This is followed by laser trimming the ladder-like resistance path 4 of the small resistive cross section for adjusting the resistance to a roughly desired value which can be shifted to a final, precise resistance of the resistor by trimming the large resistive cross section of the ladder-like resistance path 5.
Finally, the ladder-like resistance path 5 of which resistive cross section is greater than that of the ladder-like resistance path 4 hence allowing a small increase of the resistance when it is cut apart is trimmed by laser for fine adjustment to the precise resistance value. As the result, the resistor with the precise resistance will be produced.
As the resistive body pattern with the ladder-like resistance paths is being laser trimmed, its resistance van be changed to a precise value at steps. Also, as no current runs through the trimmed edge portions of the resistive body which have been affected by laser heat during the trimming, the resistor will be improved in the load-, surge- and pulse-resistant characteristics.
It is however necessary for fine adjustment to a precise resistance value in the arrangement of the conventional resistor to have the ladder-like resistance path formed greater in the resistive cross section than the main resistance path so that a change in the resistance is minimized when the ladder-like resistance path of the resistive body is trimmed. Hence, the resistive cross section of the ladder-like resistance path of the resistive body has to be increased considerably in relation to that of the main resistance path for determining a desired resistance value with tolerance of less than .+-.5%. Particularly for producing small-sized tip resistors, the ladder-like resistance path should be arranged with as possible as a minimum distance between the rungs or a minimum number of the rungs since it is hardly adjusted to have a precise value of resistance by only means of the laser trimming. It has hence been desired to develop improved resistors which have ladder-like resistance paths provided substantially identical in the size of resistive cross section to the conventional ones but are adapted for having a desired resistance determined at a higher precision thus giving higher load-, surge-, and pulse-resistant characteristics.